1. Field of the Invention
This invention relates generally to color calibration and particularly to a method and system for calibrating the colorants of a color copying and printing system.
2. Description of the Related Art
Conventionally, color copiers, printers and professional press systems create color images by combining a small number of colorants such as pigments or dyes in response to image data. For example, conventional color systems produce an image by combining cyan, magenta, yellow and black (CMYK) colorants. The same CMYK image data printed using different color reproduction systems can produce images which have different color characteristics. The different color characteristic are due to different absorption spectra of the colorants, different amounts (densities) of the colorants, and different mixing characteristics (trapping) of the colorants.
Color copiers and printers are sometimes used in the color publishing market as prepress design tools to preview color images. When used as a prepress design tool, color copiers and printers (collectively "printers") are adjusted to simulate standard press conditions so that the colors in the locally printed image closely match the colors which result when the data file is printed using standard press conditions. In order to match the printer color characteristics to those of a standard press process, a full color characterization is conventionally performed on a printer model to define the resulting color over a range of colorant densities and combinations. Once a full color characterization is determined for a printer model, image data is adjusted prior to printing to simulate standard press conditions.
Full color characterization is conventionally performed on a single printer or on several of the same model type to determine the color characterization that will be assumed for each printer of the given model type. Even though a given printer will have the same general color characterization, each model can have variances from the assumed characterization. These variances are attributable to many factors including: environmental conditions (e.g., humidity, temperature), the condition of the colorant applicators and the individual adjustments that have been made in servicing the specific printer. In order to compensate for color variances of individual printers within a model type and for printer color variance over time, color calibration techniques are used to calibrate image data to compensate for the color variance as measured specific to the printer.
One conventional characterization/ calibration system uses a generalized approach to characterize and calibrate a variety of printers and scanners to be used in various combinations. This generalized approach compensates for colorant mixing effects (in the printing process) and color decomposition effects (during the scanning or image input process) to color match printed images to input images, for each printer and scanner combination to be used. This conventional approach requires the use of a linear intermediate color space during the printing process which adds computation time and complexity.
Other conventional calibration techniques require the use of special equipment such as a densitometer. Calibration systems requiring the use of a densitometer are undesirable because densitometers are costly and because these conventional calibration systems also require a sophisticated user to perform many steps in the calibration process manually.
Thus, there is a need for a high speed calibration method and apparatus for calibrating image data to match the measured color characteristics of a specific color printer without requiring use of a densitometer and which does not require a sophisticated user.